“Traction” is a general term used to describe the ability of a shoe outsole to resist sliding motion over a surface contacted by that outsole. Traction is particularly important in athletic footwear. For example, basketball, tennis and numerous other activities often require an athlete to engage in rapid sideways motion. A secure, non-sliding contact between such an athlete's footwear and a playing surface is thus important. Without secure, non-sliding contact, the athlete's foot can slip. Such slipping will often affect the quality of the athlete's performance, and can even cause injury.
Footwear for some sports can employ cleats, spikes or other surface-penetrating mechanisms to increase traction. For many activities, however, friction between an outsole and a playing surface is the only mechanism that prevents a shoe from slipping. In such cases, increasing traction requires increasing the friction between an outsole and the playing surface(s) on which a shoe with that outsole will be used. Typically, outsoles for athletic footwear are formed from synthetic rubber and/or some other elastomeric material. Softer elastomeric materials generally have higher frictional coefficients and provide better traction, but tend to wear quickly on concrete and other rough surfaces. Harder elastomeric materials tend to have lower frictional coefficients and provide less traction, but tend to be more durable.
Certain types of playing surfaces (e.g., indoor hardwood floors) may be relatively smooth and non-abrasive. Because these surfaces impart less wear on an outsole, softer outsole materials may wear less quickly when used on these surfaces. If a shoe will only be used on hardwood or other smooth surface, it may be practical to use softer outsole materials to increase traction. Other types of playing surfaces (e.g., concrete) are more abrasive and can result in more rapid outsole wear. If a shoe will be worn on concrete or another abrasive surface, a harder outsole material with poorer traction may be preferable to a softer outsole material that would wear too quickly. For many persons who may play a particular sport on both types of surfaces, however, owning two pairs of athletic shoes may be inconvenient and/or economically impractical.